The plea deal allows Thatcher, the son of former British Prime Minister Margaret Thatcher, to leave South Africa and to rejoin his family in the United States. Within hours, Mark Thatcher arrived at Cape Town's international airport and was whisked to a VIP section.

Mark Thatcher admitted in the Cape High Court that he paid $275,000 in two installments last year to charter an Alouette III helicopter, which mercenaries planned to use in their botched takeover. But he said in court documents that he was told it would be used for commercial purposes.

Thatcher acknowledged in the documents that he began to suspect the helicopter would be used for military reasons before he made the payments.

"Although the helicopter was never used in any such mercenary activity, and in fact did not leave southern Africa, Sir Mark had by then committed an attempt to contravene the provisions of" South Africa's anti-mercenary laws, his lawyer George van Niekerk said in a statement.

Thatcher's wife, Diane, the daughter of a wealthy Texas auto dealer, flew to Dallas with their two children shortly after his August arrest.

Mark Thatcher refused to answer questions before he was whisked home in a green BMW. Across the street, a poster reading "Save me mummy" hung from a window.

Lady Thatcher expressed relief Thursday that the case against her son was concluded.

"This has been a difficult time for all of the family," she told Britain's domestic news agency the Press Association. "Obviously I am delighted that it has been brought to an end."

Mark Thatcher, who has lived in South Africa since 1995, was arrested at his suburban Cape Town home on Aug. 25 and charged with violating this country's Regulation of Foreign Military Assistance Act.

He also faces charges in Equatorial Guinea, where 19 other defendants already are on trial in connection with an alleged plot last year to overthrow President Teodoro Obiang Nguema, who has ruled Africa's third-largest oil producer for the past 25 years.

Equatorial Guinea alleges Thatcher and other mainly British financiers worked with the tiny country's opposition figures, scores of African mercenaries and six Armenian pilots in a takeover attempt foiled in March.

Simon Mann, Thatcher's friend and a former British special forces commander accused of masterminding the plot, approached Thatcher in November 2003 to join what he described as a transport venture in West Africa, according to court documents. Mann later put Thatcher in touch with Crause Steyl, who operates an air ambulance company and chartered the helicopter Thatcher paid for, the documents said.

Mann was arrested and convicted with 67 alleged accomplices in Zimbabwe on weapons and other minor charges. A Zimbabwe judge agreed Thursday to reduce Mann's seven-year prison sentence by three years, lawyers said.

Steyl was among three others who later pleaded guilty to violating South Africa's anti-mercenary laws.

"It should be noted that Sir Mark was not charged with any involvement in the attempted coup d'etat in Equatorial Guinea," van Niekerk said. "The plea bargain was entered into solely as a result of his financing of the charter of a helicopter in circumstances where he should have exercised more caution."

The court ordered Thatcher to answer questions submitted by Equatorial Guinea under oath in November, but that appearance was postponed until Feb. 18 to give his lawyers a chance to appeal.

Thatcher's legal team has not indicated whether it will proceed with an appeal.

In the United States, where he married in 1987, Thatcher settled a civil racketeering lawsuit for an undisclosed sum and faced charges from the Internal Revenue Service stemming from a role with a home security company that went bankrupt.

He was scrutinized by Britain's Parliament in 1994 over reports that he was involved in arms sales to Saudi Arabia and Iraq while his mother was prime minister  allegations he denied.